In current aerospace applications electrical power is generated using traditional wound-field synchronous electrical machines. These synchronous electrical machines are coupled to a rotor of the gas turbine engine using a complex mechanical transmission system, for example a radial drive shaft from the gas turbine engine rotor and a gearbox. These synchronous electrical machines are mounted on the gas turbine engine in a position where they are readily accessible for maintenance and/or replacement if there is a fault with the synchronous electrical machine.
It is proposed to embed the synchronous electrical machine in the gas turbine engine, for example the rotor of the synchronous electrical machine is coupled to the rotor of the gas turbine engine. The advantage of the embedded synchronous electrical machine is that it allows the complex mechanical transmission system to be removed, or greatly simplified, providing significant operational and efficiency benefits. However, these embedded synchronous electrical machines are difficult to remove and replace if there is a fault/failure. EP0659234B1 discloses the use of coupled synchronous electrical machines and embedded synchronous electrical machines in gas turbine engines.
It is desirable to use the synchronous electrical machine to start the gas turbine engine, as well as to generate electricity, as this removes the reliance on an air starter and provides additional engine design benefits. A power electronic interface is provided with the synchronous electrical machine to enable the synchronous electrical machine to act as a motor rather than a generator. Electrical generator systems utilising power electronic converters enable very high power dense machine technologies, for example permanent magnet designs to be employed in the asynchronous electrical machine, which gives further size and weight benefits compared to traditional synchronous electrical machines.